Display screen or a portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface showing our new design; and,

FIG. 2 is a front view of a second embodiment thereof.

The broken line showing of the display screen or portion thereof with graphical user interface is included for the purpose of illustrating the article and forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 